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Statement (I): When waste water is treated at an oxidation ditch, anaerobic sludge digester is not required. Statement (II): Oxidation ditch admits an extended aeration process whereby sludge gets mineralized.

Statement (I): When waste water is treated at an oxidation ditch, anaerobic sludge digester is not required. Statement (II): Oxidation ditch admits an extended aeration process whereby sludge gets mineralized. Correct Answer Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)

The conventional activated sludge plant is modified to eliminate the primary sedimentation tank and sludge digestion tank, in a process, called extended aeration process (also called oxidation ditch).

In this, an aeration tank of longer aeration time is provided.  A some part of settled sludge is re-circulated back and excess settled sludge which is well stabilised due to long detention period of 12-15 hours  can be easily dried on sand beds and disposed of suitably without using any sludge digestion tank.

Important Point:

Design parameters for an oxidation ditch are:

1. Detention time: 12-15 hours.

2.  Volume of Ditch - 120 to 150 cum per metre length of rotor.

3.  Mixer Liquor suspended solids (MLSS) concentration: 4000-5000 mg/l.

4. BOD removal: 98 % and Suspended solids removal: 95 %.

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